共查询到20条相似文献,搜索用时 125 毫秒
1.
用高斯程序的B3LYP交换相关函数和全电子基组DGDZVP、TZVP优化了Nin、Nin+和Nin-(n=2~8),得到了这些体系的基态几何构型、离化能、电子亲和能以及键能.结果表明:Ni2,Ni3,Ni4,Ni5和Ni6团簇的基态分别是5,7,9,11和13重态.表明:Ni2,Ni3,Ni4,Ni5和Ni6团簇中分别有4,6,8,10和12个平行自旋的电子,在每一个Nin团簇中非耦合的电子是最多,这些电子占据不同的轨道,导致每一个Nin团簇的能量最小,说明在这些Nin团簇中电子平行的效应大于电子耦合的效应,这显然与d电子的离域效应有关,这被称为自旋极化效应,符合宏特规则.Nin、Nin+和Nin-(n=2~8)体系的磁矩分别是Nin具有8μB(n=6~8),Nin+具有9μB(n=6~8),Nin-具有7μB(n=4~8). 相似文献
2.
在相对论有效原子实势近似下,用密度泛函理论方法,对Pdn(n=2,3,4),Yn(n=2,3,4),PdnY(n=1,2,3,4),PdYn(n=2,3,4),Pd2 Yn(n=2,3,4)团簇的各种可能的几何构型进行全优化计算,得到它们的基态结构和 光谱性质.结果表明,由于 Jahn-Teller效应, Pd4和Y4的基态结 构为Cs构型,P d3和Y3为C2v 构型;混合微团簇Pd3Y,Pd 4Y,PdY3,PdY4 和 Pd2Y4基态为Cs构型.最后计算了团簇的能级分布和最 高占据轨道与最低空轨道之间的能级间隙,分析了团簇的化学活性.
关键词:
Pd-Y团簇
有效原子实势
密度泛函 相似文献
3.
用高斯程序的B3LYP交换相关函数和全电子基组DGDZVP、TZVP优化Nin、Nin+和Nin-(n=2~8),得到这些体系的基态几何构型、离化能、电子亲和能及键能.结果表明:Ni2,Ni3,Ni4,Ni5和Ni6团簇的基态分别是5,7,9,11和13重态.表明:Ni2,Ni3,Ni4,Ni5和Ni6团簇中分别有4,6,8,10和12个平行自旋的电子,在每一个Nin团簇中非耦合的电子最多,这些电子占据不同的轨道,导致每一个Nin团簇的能量最小,说明在这些Nin团簇中电子平行的效应大于电子耦合的效应,这显然与d电子的离域效应有关,称为自旋极化效应,符合宏特规则.Nin、Nin+和Nin-(n=2~8)体系的磁矩分别是Nin具有8μB(n=6~8),Nin+具有9μB(n=6~8),Nin具有7μB(n=4~8). 相似文献
4.
本文提出了予测稠苯芳烃及其衍生物的环上和烷基链上质子化学位移的计算方法。
将稠苯芳环化合物用凯库勒式表示,用下式计算:
δ=σj.c-c+σmi.ci
σj.c-c为各种乙烯基的效应。σmi.ci,为各个苯环的六电子π轨道的净环流效应,其计算式为:
σm.e=(1/2)m×1,52 m=n-u
m为净环流效应级数,等于质子到该苯环相隔的键数n减其中的顺式键数u。
在菲环和类似菲环的4,5位与9,10位质子需考虑菲环效应。蒄环上的质子需考虑蒄环效应。有取代基需考虑取代基的效应。
计算环上烷基质子的公式:
δ=σp.CH3+ασ2.CH3+βσt.CH3+σi.G
此公式在作者以前的文章中己经报道。σi,G为稠苯芳基的某级效应。 相似文献
5.
本文应用Fenlon理论研究了当频率为f1的弱声信号与频率为f2=2f1的泵浦声信号,在非线性相互作用时出现的弱声信号被放大的简并参量放大过程。结果表明,这种放大效应与信号的初位相差(φ2-2φ1)有明显依赖关系,例如当φ1=π/2,φ2=0或φ1=0,φ2=π时可得弱声信号的最大增益,φ1,φ2为弱声和泵浦声的初位相。实验验证是在直径为5cm、长为13m的行波管中进行。实验中研究了不同距离处弱声信号的放大量与初位相差的关系,发现当φ1=π/2或φ2=π时的最大增益为1.8-2dB;实验中还研究了在最大和最小增益的初位相差时弱声信号放大量与距离的关系,所得实验结果与理论吻合较好。 相似文献
6.
本文提出了予测稠苯芳杂环及其烷基链上质子化学位移的计算方法。
将稠苯芳杂环化合物用凯库勒式表示,计算式为为需考虑的苯环内的乙烯基效应。σmi,ci为各苯环的环流效应。σ1,Hc为各芳杂环的屏蔽效应,对杂环上质子它就是该单独芳杂环上相应质子的δ值,对苯环上质子要将它分解为各结构因素的效应,即:σ1,He=(1/2)d-1δx=y(或σz)+σc-c·σm,H.
σx-y与σz为杂原子或其基团的屏蔽效应,σc=c为存在于芳杂环中的乙烯基的效应,σm,Hc为芳杂环的环流效应,d为对不同质子所考虑的键数。有取代基时需考虑取代基的效应。计算环上烷基质子的公式为:δ=σp,CH3+ασc,CH3+βσt,CH3+σl,G
σl,G为稠苯芳杂环基的某级效应。 相似文献
7.
拓扑超导体自身具有对量子退相干天然的免疫性以及可编织性,这使得它在现代量子计算领域中受到了越来越多的重视,并且成为了下一代计算技术中最有希望的候选者之一。由于拓扑超导态在固有拓扑超导体中相当罕见,因此,当前大部分实验上的工作主要集中在由s波超导体与拓扑绝缘体之间通过近邻效应所诱导的拓扑超导体上。本论文中,我们回顾了基于拓扑绝缘体/超导体异质结的拓扑超导体的研究进展。在理论上,Fu和Kane提出,通过近邻效应将s波超导体的能隙引入到拓扑绝缘体,可以诱导出拓扑超导电性。在实验上,我们也回顾了一些不同体系中的拓扑超导近邻效应的研究进展。文章的第一部分,我们介绍了一些异质结,包括:三维拓扑绝缘体Bi2Se3和Bi2Se3与s波超导体NbSe2以及d波超导体Bi2Sr2CaCu2O8+δ的异质结,拓扑绝缘体Sn1-xPbxTe与Pb的异质结,二维拓扑绝缘体W... 相似文献
8.
本文报道,通过对Y1-xCaxBa2Cu3-xMxO7-δ(M=Fe,Ni)体系样品的晶体结构、氧含量、正常态电阻率与温度的关系,以及超导转变温度等测量,并与YBa2Cu3-xMxO7-δ(M=Fe,Ni)体系进行比较,发现Y1-xCaxBa2Cu3-xFexO7-δ体系的Tc显著地高于相应x值的YBa2Cu3-xFexO7-δ体系,而Y1-xCaxBa2Cu3-xNixO7-δ体系则相反,Tc低于仅Ni替代的体系,表明Ca和Fe同时替代时两者引起的载流子浓度(nH)变化相互补偿,抑制了仅Fe替代时引起的nH和Tc急剧下降;而作Ca和Ni同时替代时主要的不是两者引起载流子浓度变化的相互补偿,Ca和Ni替代效应之间的关联较弱。作者认为,对Y1-xCaxBa2Cu3-xFexO7-δ体系属于CuO2平面外的元素替代,这时载流子浓度是决定Tc的主要因素;而对Y1-xCaxBa2Cu3-xNixO7-δ体系,由于Ni2+离子主要占据Cu(Ⅱ)位,它导致磁拆对效应,Ni2+离子的拆对效应是引起Tc下降的直接原因。
关键词: 相似文献
9.
10.
我们用缀饰模型研究强近共振激光脉冲驱动下二能级系统与弱试探脉冲的相互作用。当试探脉冲的频率ω2调到共振频率ω2=ω1±<Ω21D>时,试探脉冲呈现吸收或放大效应。还得到非线性混频效应的瞬态过程。共振增强存在于此非线性混频过程中。
关键词: 相似文献
11.
D. Bhoi P. Mandal P. Choudhury S. Dash A. Banerjee 《Physica C: Superconductivity and its Applications》2011,471(7-8):258-264
The magnetization of the PrFeAsO0.60F0.12 polycrystalline sample has been measured as functions of temperature and magnetic field (H). The observed total magnetization is the sum of a superconducting irreversible magnetization and a paramagnetic magnetization. Analysis of dc susceptibility χ(T) in the normal state shows that the paramagnetic component of magnetization comes from the Pr3+ magnetic moments. The intragrain critical current density (JL) derived from the magnetization data is large. The JL(H) curve displays a second peak which shifts towards the high-field region with decreasing temperature. In the low-field region, a plateau up to a field H* followed by a power law H?5/8 behavior of JL(H) is the characteristic of the strong pinning. A vortex phase diagram for the present superconductor has been obtained from the magnetization and resistivity data. 相似文献
12.
将Fourier-Bessel级数引入KZK方程的求解,用于计算黏滞媒质中零阶Bessel型超声场的二次谐波声场,得到其级数形式的解析解,并由此得出二次谐波声场在近场分布的一个新结论.设声源表面声压分布为J0(α0r),则二次谐波声压在近场的径向分布服从J20(α0r)函数规律.这一结论合理解释了相关的实验结果,表明二次谐波声场在近场和远场有不同的径向分布,从而解决了非线性Bessel型超声场二次谐波的近场分布问题.研究还发现二次谐波声场具有类似基波声场的有限衍射特性.给出了一个数值计算和仿真实例. 相似文献
13.
本文从理论上讨论了晶场作用对稀土离子能级重心位移的影响,具体计算了J混效应对15个含Nd3+离子的晶体中的4IJ能级重心的位移。结果指出J混效应加宽了光谱项2S+1L由于自旋轨道耦合导致的能级劈裂宽度,并且与晶体基质的组成、结构有关。
关键词: 相似文献
14.
15.
We report high resolution infrared absorption spectra of LiYF4-Ho exhibiting well resolved nuclear hyperfine structure (hfs). The halfwidths of some hfs components do not exceed 0.03 cm?1. Magnetic field at the nucleus is evaluated. Non-radiative relaxation rates due to phonon emission are estimated. With the help of experimentally found 〈Γ3|Jz|Γ3〉 matrix elements g-factors of the excited crystal field levels are calculated. Some hfs peculiarities are discussed. 相似文献
16.
《Current Applied Physics》2002,2(3):261-268
La0.667Ca0.333Mn1−xMxO3−δ (M=Mg, Li or Re) exhibit insulating behaviour and nonlinear current–voltage (J–E) relationship with voltage-limiting characteristics at temperatures below the ferromagnetic transition (Tc). The high current region is set in at field strengths <60 V/cm. Nonlinearity exponent, α in the relation J=kEα increases inversely with temperature. In presence of an external magnetic field, the J–E curves show higher current density at lower field strengths. Microstructural studies indicate that there is no segregation of secondary phases in the grain boundary regions. There is remarkable changes in ρ(T) as well as J–E curves with the grain size. Annealing studies in lower pO2 atmospheres indicate that there is significant out-diffusion of oxygen ions through the grain boundary layer (GBL) regions creating oxygen vacancies in the GBL regions. The concentration of Mn4+ ions is lowered at the GBL due to oxygen vacancies, reducing the probability of hopping and resulting in insulating behaviour. Therefore an insulating barrier is introduced between two conducting grains and the carrier motion between the grains is inhibited. Thus below Tc, where sufficient increase in resistivity is observed the conduction may be arising as a result of spin dependent tunneling across the barrier. External electric field lowers the barrier height and establishes carrier transport across the barrier. Above certain field strength, barrier height diminishes significantly and thereby allowing large number of carriers for conduction, giving rise to highly nonlinear conductivity. 相似文献
17.
18.
19.
《Solid State Communications》1987,61(6):401-404
Steplike magnetization vs magnetic field dependence obtained in pulsed magnetic field up to 34 T in 1.8 K enables us to determine the value of the antiferromagnetic exchange constant between nearest-neighbour Mn2+ ion (J1). The analysis of the first and the second step position in the framework of a generalized cluster model [1] yields J1 = −8.6±0.9 K for Cd0.945Mn0.055 S and J1 = −9.9±0.9 K for Zn0.95 Mn0.05 Se. 相似文献
20.
Ratan Lal 《Physica C: Superconductivity and its Applications》2010,470(4):281-284
The critical current density Jc of some of the superconducting samples, calculated on the basis of the Bean’s model, shows negative curvature for low magnetic field with a downward bending near H = 0. To avoid this problem Kim’s expression of the critical current density, Jc = k/(H0 + H), where Jc has positive curvature for all H, has been employed by connecting the positive constants k and H0 with the features of the hysteresis loop of a superconductor. A relation between the full penetration field Hp and the magnetic field Hmin, at which the magnetization is minimum, is obtained from the Kim’s theory. Taking the value of Jc at H = Hp according to the actual loop width, as in the Bean’s theory, and at H = 0 according to an enhanced loop width due to the local internal field, values of k and H0 are obtained in terms of the magnetization values M+(?Hmin), M?(Hmin), M+(Hp) and M?(Hp). The resulting method of estimating Jc from the hysteresis loop turns out to be as simple as the Bean’s method. 相似文献